1. Field of the Invention
The present invention relates to a brake device.
2. Description of Related Art
JP-A No. 2007-182122 describes one type of brake devices. As shown in FIG. 1 of JP-A No. 2007-182122, the brake device has a driving fluid pressure chamber (external fluid pressure chamber 90p) that drives a master piston (rear master piston 62) and a pressure booster 90 that is connected to the driving fluid pressure chamber. The pressure booster 90 has a fluid pressure source 90a and a fluid pressure controller 90b, which are controlled by an electronic controller 13. The fluid pressure controller 90b has proportional solenoid valves 96a, 96b of a normally close type for pressure boost that are provided in parallel to each other on a fluid passage connected to a boost pressure port 16P of a master cylinder 60 from the fluid pressure source 90a, a proportional solenoid valve 97 of a normally open type for pressure reduction that is provided on a fluid passage connected to a pump reservoir 91 of the fluid pressure source 90a from the boost pressure port 16P, and a proportional solenoid valve pressure gauge 95b that monitors pressure of the boost pressure port 16P.
According to the above-described brake device, a brake fluid is supplied from the fluid pressure source 90a to the external fluid pressure chamber 90p through the proportional solenoid valves 96a, 96b of a normally close type for pressure boost. However, in general, flow rates per unit time of the proportional solenoid valves are relatively low. Accordingly, when high braking force is abruptly required in braking a vehicle, a supply amount of the brake fluid for driving the master piston becomes smaller than a desired amount, so that the sufficient braking force may not be provided in good responsiveness to the braking. In response, it can be considered to make a configuration of increasing the flow rates of the proportional solenoid valves or increase the number of proportional solenoid valves to be provided. However, in this case, the brake device would be enlarged and the cost would be increased.